Diophantine approximation on Veech surfaces

We show that Y. Cheung's general $Z$-continued fractions can be adapted to give approximation by saddle connection vectors for any compact translation surface. That is, we show the finiteness of his Minkowski constant for any compact translation surface. Furthermore, we show that for a Veech surface in standard form, each component of any saddle connection vector dominates its conjugates. The saddle connection continued fractions then allow one to recognize certain transcendental directions by their developments

Ergodicity for Infinite Periodic Translation Surfaces

For a Z-cover of a translation surface, which is a lattice surface, and which admits infinite strips, we prove that almost every direction for the straightline flow is ergodic

New strategies in Bioconjugation : chemical modification of nucleic acids and peptides

One of the open challenges in chemical biology is to identify reactions that proceed with large rate constants in water at neutral pH values. Once assembled, these conjugates may be used for a broad variety of applications (e.g., therapeutics, imaging probes or as a catalytic system). Herein we describe a novel approach for the chemical modification of nucleic acids using guided organometallic-catalysts. Customized dirhodium complexes were prepared using modular ligands bearing various functional groups and connected to peptide nucleic acids through stable oxime linkages. The final constructs have been optimized for aqueous catalysis and were tested in preliminary alkylation studies of single-stranded DNA via dirhodium-carbenoids generated from alpha-diazocarbonyl compounds. During the course of optimizing the rather slow kinetics of oxime formation, we have developed two highly efficient methods for rapid oxime-based bioconjugations. (1) Dialdehydes were found to react with O-alkylhydroxylamines at rates of 500 M-1 s-1 in neutral aqueous buffer in the absence of a catalyst. The key to these conjugations is an unusually stable cyclic intermediate, which ultimately undergoes dehydration to yield an oxime. The scope and limitations of this method are outlined, as well as its application in bioconjugation with a DNA 41-mer and a mechanistic interpretation that will facilitate further developments of reactions with O-alkylhydroxylamines at low substrate concentrations. (2) Oximes proximal to boronic acids form in neutral aqueous buffer with rate constants of more than 104 M−1 s−1, the largest to date for any oxime condensation. The reaction tolerates a variety of biological interfering additives and is suitable for the rapid modification of short peptide sequences. Once formed, the oxime products are stable for days and undergo slow interconversion through a hydrolysis-based mechanism. Boron's dynamic coordination chemistry confers an adaptability that seems to aid a number of elementary steps in the oxime condensation. In conclusion both methods represent important improvements for oxime-based bioconjugations in water (pH 7) at low equimolar concentrations. The high reaction kinetics are achieved without the need for additional reagents, catalysts or variations of the reaction conditions. In addition, the possibility of using reacting pairs that are commercially available will greatly enhance the applicability of these methods for efficient conjugations of precious biomolecules in the future

Transferência de dispositivos de reconhecimento da agricultura orgânica e apropriação local: uma análise sobre a Rede Ecovida

Recognition mechanisms for organic agriculture have been transferred from the European Union and the United Sates of America to Brazil, along with their regulation and certification systems. Our research aims to evaluate the local adaptation and appropriation of such systems in the state of Santa Catarina, Brazil. This work is a preliminary analysis of field data collected from one of the three networks surveyed, "Rede Ecovida de Agroecologia". This network is set up to escape, as far as possible, from constraints established by a kind of recognition its members define as "official", belonging to the"certification industry", and exceedingly reductionist. The network gives, therefore, priority to direct sales to "aware" consumers. This militant practice constitutes an ambitious form of social control ofcertification, but their procedures have been situated, for a long time, in the relatively narrow space of local markets. They are confronted, however, to other options linked to wider markets with shorter action time spans, that reflect the reactivity of commercial operators to rapid changes in urban consumption models. The duration, stability and flexibility of each of these recognition systems depend largely on the dynamic imposed on the temporal and spatial contexts of their agents

Lanthanide grafted phenanthroline-polymer for physiological temperature range sensing

Accurate measurement of the temperature is crucial as it determines the dynamics of almost any system. Conventional contact thermometers are not well suited for small scale measurements. Temperature dependent luminescent materials, i.e. materials that emit light of different color at different temperature, are therefore of particular interest in the development of noncontact thermometers. Luminescent materials consisting of lanthanide ions feature high thermal sensitivity, high photostability and high quantum yields. These ions possess very interesting light emitting properties. By anchoring them onto different backbone materials, their light absorption is increased. The search for a backbone that allows the sensor to be active in a defined temperature range, with a high detection sensitivity is ongoing. This work reports the first insoluble phenanthroline-polymer (phen-polymer) backbone on which europium (Eu3+) and terbium (Tb3+) trifluoroacetylacetone (tfac) complexes are easily grafted in a 1 : 1 metal ratio in order to create a noncontact temperature sensor. Two clear, discriminable emission peaks were observed during the photoluminescence study at room temperature, demonstrating that this material can be used as a ratiometric thermometer. The characteristic emission peak correlated to Eu3+ transition is slightly stronger than the emission peak of Tb3+ transition, resulting in a yellow emission color. The maximum value of the relative temperature sensitivity was calculated to be 2.3404% K-1 (340 K), which indicated good thermometric behavior. The emission color of the designed phen-polymer@Eu,Tb_tfac changed from light green (260 K) to orange-red (460 K). The thermometer can therefore be used as a ratiometric noncontact temperature sensor in the broad physiological temperature range

Comparison of boron-assisted oxime and hydrazone formations leads to the discovery of a fluorogenic variant

We use kinetic data, photophysical properties, and mechanistic analyses to compare recently developed high-rate constant oxime and hydrazone formations. We show that when Schiff base formation between aldehydes and arylhydrazines is carried out with an appropriately positioned boron atom, then aromatic B–N heterocycles form irreversibly. These consist of an extended aromatic structure amenable to the tailoring of specific properties such as reaction rate and fluorescence. The reactions work best in neutral aqueous buffer and can be designed to be fluorogenic – properties which are particularly interesting in bioconjugation